This invention relates to the preparation of perfluoroalkylether (PFAE) tertiary alcohols and the chemical intermediates useful in their preparation. The invention also relates to use of such alcohols and their intermediates as antiwear additives for perfluorinated fluids.
Highly fluorinated compounds have long been of interest because of their excellent potential for high temperature applications. Fluids based on perfluoropolyalkylethers (PFPAE) have, in addition to high thermal and oxidative stability, a wide liquid range which make them ideal candidates for aerospace applications. These fluids consist essentially of a mixture of linear fluorinated polyethers. These fluids have the general formula: EQU R.sub.f O(Z).sub.m (Y).sub.n R.sub.f
wherein R.sub.f is a lower perfluoroalkyl group, such as CF.sub.3, C.sub.2 F.sub.5, C.sub.3 F.sub.7 and the like, wherein Z is --CX.sub.2 CX.sub.2 O--, --CX.sub.2 CX.sub.2 CX.sub.2 O-- or --CX.sub.2 OCX.sub.2 CX.sub.2 O--, where X is --F, --CF.sub.3, --C.sub.2 F.sub.5 and the like, and Y is --CFXO--, m and n are integers whose sum is between 2 and 200 and the ratio of n to m is between 0.1 and 10, and wherein the Z and Y units are statistically distributed along the PFPAE chain. Commercial base fluids of this type have been available for some time, for example, Krytox.RTM. (DuPont), Fomblin.RTM. (Montedison), Demnum.RTM. (Daikin) and the like. Their practical utility in aerospace and military applications has been hampered by the wear and corrosion of certain metal components exposed to these base fluids under extreme conditions.
Deficiencies in base fluids are generally removed and the performance of the fluids improved by the use of additives. Conventional additives developed for the improvement of a variety of specific properties of hydrocarbon base fluids are generally not suitable for perfluorinated fluids. These conventional additives are not soluble in perfluorinated fluids and are ineffective. One way of overcoming this incompatibility is to synthesize compounds containing fluoroalkylether groups plus selected functional groups for specific activity. Although this approach may make the compound soluble in a fluorinated base fluid, mere replacement of hydrocarbon groups with fluorocarbon groups can change the useful properties of the additive itself by changing the properties of the critical functional group present in the additive. These difficulties are well known to those familiar with the art. In spite of these difficulties, a few useful additives have been developed for perfluorinated fluids. One such example is the development of PFAE substituted triphenylphosphines, C. E. Snyder, Jr. and C. Tamborski, U.S. Pat. No. 4,097,388. These additives, when dissolved in PFPAE fluids, have significantly reduced the corrosion of certain metal components exposed to the fluid at high temperatures in an oxidative environment. Reducing corrosion of the metal components exposed to a PFPAE fluid is only one of the requirements for its successful application as a functional fluid in the range of -65.degree. to 700.degree. F. The problem of wear of metal components must be addressed. An antiwear additive should have sufficient solubility in the PFPAE fluid even at -65.degree. F. Another requirement is that in order to be effective for long periods of time at temperatures as high as 700.degree. F., the antiwear additive should have low volatility characteristics. Such stringent property requirements are not essential when these antiwear additives are used for other applications such as instrument oils, space lubes, etc. For instance the antiwear additives for space lubes require low vapour pressure but not high temperature stability. Thus in order to incorporate the required combination of properties in the additive for different applications, it is desirable that the methods used for the synthesis of these additives readily permit structural variations in terms of the number of active functional groups per molecule as well as the nature of the pendant groups. It is additionally desirable if the starting materials necessary for the synthesis of the aforementioned antiwear additives are readily available or can be easily synthesized.
Accordingly, it is an object of this invention to provide a novel antiwear additive for perfluoropolyalkylethers.
Another object of this invention is to provide a method for making novel antiwear additives for perfluoropolyalkylethers.
A further object of this invention is to provide perfluorinated fluids improved antiwear properties
Other objects and advantages of the invention will be apparent to those skilled in the art.